Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity.
In use, the electrode catheter is inserted into a major vein or artery, e.g., femoral artery, and then guided into the chamber of the heart which is of concern. Within the heart, the ability to control the exact position and orientation of the catheter tip is critical and largely determines how useful the catheter is.
Deflectable catheters are generally well-known. A convention catheter has a control handle with a housing having a piston chamber at its distal end. A piston is mounted in the piston chamber and is afforded lengthwise movement. The proximal end of the catheter body is attached to the piston. A puller wire is attached to the housing and extends through the piston and through the catheter body. The distal end of the puller wire is anchored in the intermediate section of the catheter. In this arrangement, lengthwise movement of the piston relative to the housing results in deflection of the catheter intermediate section.
The puller wire is typically made of a single, non-stranded metal wire, such as stainless steel or Nitinol, and is coated with Teflon® or the like. The coating imparts lubricity to the puller wire so that it can slide freely within a compression coil extending through the catheter body. The puller wire typically has a diameter ranging from about 0.006 to about 0.010 inch.
A typical method of anchoring the puller wire to the intermediate section of the catheter is by fixedly attaching, e.g., crimping, an anchor to the distal end of the puller wire. The anchor is then welded in a blind hole in a tip electrode.
Alternatively, the distal end of the puller wire is secured to the distal section of the catheter tubing. A short piece of tubular stainless steel, e.g., hypodermic stock, is fitted over the distal end of the puller wire and crimped to fixedly secure the puller wire. The distal end of the tubular stainless steel is fixedly attached, e.g., by welding, to a stainless steel crosspiece, which fits into a notch formed in the outer wall of the tubing. The portion of the notch not occupied by the crosspiece is filled with glue, or the like, such as a polyurethane glue that is harder than the material of the flexible tubing. With conventional crimping methods, the cross-sectional area of the crimped portion of the puller wire can be significantly decreased, thereby excessively weakening the puller wire.
While these methods are generally effective in securing the distal end of the puller wire, both crimping and soldering tend to weaken the puller wire, thereby subjecting the puller wire to fatigue and premature breakage.
Another typical method of anchoring the puller wire to the intermediate section and the housing is to wrap the wire around an anchor pin. Thus, in general, when a puller wire is used in a wrapped configuration whether for anchoring its distal end, or even around a pulley in a control handle for greater throw in the deflection of the catheter, the puller wire tends to work-harden in a wrapped position, leading to a loss in elasticity and premature breakage.
Accordingly, there is a desire for an improved puller element that can be manipulated by conventional control handles for deflecting catheters and yet be suited for attachment at its distal end in a manner that causes less fatigue and premature wearing. It is also desirable that such improved puller element retain more of its elasticity during repeated use and have overall better durability for use with control handles that provide more throw or employ pulley mechanisms to manipulate deflection of the catheter.